This invention relates to the treatment of sewage, and particularly a process and apparatus for gasification and drying sewage sludge in an offshore facility.
Raw sewage is a very dilute liquid containing as much as 99.95% water. The low concentration of impurities makes purification of sewage costly. As a result, disposal of sewage without treatment has long been practiced. Increases in the volume of sewage, brought on by increased population and industrialization, have led to increased numbers of sewage treatment facilities, with a corresponding commitment of land and economic resources.
In a conventional sewage treatment facility, raw sewage is separated by screening, filtration, and sedimentation into a liquid effluent and sludge. The effluent contains water and dissolved materials, and is generally discharged from the sewage treatment facility. The sludge may then be subjected to anaerobic digestion by various species of microorganisms. This digestion tends to break down complex organics in the sludge and produce methane gas along with some hydrogen sulfide which may be burned for process heat or sold. The residual sludge may then be discharged, or in some cases it is dried and then used as fertilizer or burned.
Each of the procedures associated with conventional sewage treatment; especially sedimentation tanks, trickling filters, digester tanks and drying beds; requires substantial area. Further the building of a facility requires substantial capital investment at a very low rate of return.